A production process of a tuning fork resonator (hereinafter referred to as a resonator) includes a step of adjusting an oscillation frequency. As a conventional resonator frequency adjusting method for this step, a method for adjusting the frequency of a resonator is disclosed in, for example, JP 2002-164759A.
A resonator disclosed in JP 2002-164759A is provided with a piezoelectric element (hereinafter referred to as an element) there within. The element includes a base portion and two leg portions. In addition, a metal film is provided on the top and bottom major surfaces of the two leg portions so as to adjust frequency.
In the resonator frequency adjusting method of JP2002-164759A, an oscillation frequency is adjusted by removing a portion of the top and bottom major surfaces of the metal film, which is provided as a weight for adjusting frequency on the top and bottom major surfaces of the leg portions of the element, by laser irradiation. Specifically, the metal film is irradiated with a laser to remove a portion of the metal film, thereby increasing the oscillation frequency of the resonator. The resultant oscillation frequency is measured. Laser irradiation and frequency measurement are repeatedly performed until the measured frequency value of the resonator reaches a target value. More specifically, when a YAG laser or the like is used, a portion of a metal film having a diameter of about 20 μm is removed by laser irradiation of a point on the metal film, resulting in a removal region (hereinafter referred to as a removal dot). Thus, the oscillation frequency of the resonator is increased by 2 to 3 ppm. Thus, each laser irradiation increases the oscillation frequency of the resonator by 2 to 3 ppm. The oscillation frequency is measured after each laser irradiation. When the measured frequency reaches a target value, the frequency adjustment procedure is ended.
In the above-described frequency adjusting method, the metal film on the top and bottom major surfaces of the leg portion is irradiated with a laser in a direction perpendicular thereto. Therefore, a plurality of removal dots are formed when rough adjustment is performed. Particularly when there is a relatively large difference between the oscillation frequency before adjustment and a target frequency, a large number of removal dots need to be formed. Unfortunately, in the above-described frequency adjusting method, the frequency adjustment procedure for the metal film on a limited region of the top and bottom major surfaces of the leg portion becomes unstable or the production efficiency of the resonator is decreased, in proportion to an increase in the number of removal dots.
Also, recently, there has been a demand for further miniaturization of resonators. In association with this, a smaller element is desired to be provided in a resonator. As the size of an element is reduced, the region of metal film for adjustment is also decreased. Therefore, it is difficult to use conventional resonator frequency adjusting methods to provide a large metal film frequency adjustment amount (rough adjustment) in a limited region of metal film for adjustment.
The present invention is provided to solve the above-described problems. It is an object of the present invention to stabilize the frequency adjustment procedure of the method for adjusting an oscillation frequency of a resonator by removing a portion of a metal film formed on the surface of an element, even if it is small, by beam irradiation, and to improve the production efficiency of the resonator.